1. Field of the Invention
The present invention relates to a technology for measuring and controlling solid concentration of a liquid containing solid content.
2. Description of the Related Art
There has been proposed an image forming apparatus that forms an image on a recording medium such as a sheet of paper using a liquid toner. The liquid toner is a liquid containing solid content, that is, a liquid in which particles or the like containing colorants as the solid content are contained in silicone oil (carrier liquid). For the liquid toner, toner concentration (wt %) or solid concentration, which is a ratio of the solid content such as toner particles to the silicone oil, is important. This is because the change in the solid concentration of the liquid toner largely affects the quality of the image formed on the sheet, which makes it difficult to keep the stable quality. Therefore, conventionally, a solid-concentration measuring apparatus that measures solid concentration of a liquid toner is proposed.
A conventional solid-concentration measuring apparatus is disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-270959. The conventional solid-concentration measuring apparatus is configured to provide a solid-concentration measuring apparatus, which includes a concentration detecting roller, in a toner tank and to form a toner layer on the concentration detecting roller with a liquid toner retained in the toner tank. A reflection intensity of the toner layer formed on the concentration detecting roller is detected by an optical sensor, and the solid concentration is measured based on the reflection intensity.
The conventional solid-concentration measuring apparatus, however, measures the solid concentration based on the reflection intensity of the toner layer, and the measurement is thereby largely affected by a state of the toner layer and a surface state of the concentration detecting roller. Because the temperature causes the viscosity of the liquid toner to change, a transfer amount of the liquid toner to the concentration detecting roller changes depending on the temperature. Moreover, a nip pressure of the roller changes caused by variation in precision of components such as the roller. Therefore, it may be impossible to form the toner layer with uniform thickness. Furthermore, the surface of the concentration detecting roller may be changed caused by roller wear. As explained above, the conventional solid-concentration measuring apparatus is affected by these disturbances, and the measurement precision of the solid concentration is thereby insufficient.